Touch-sensitive user interfaces that include touch-sensitive sensing areas are used in many types of devices. In some existing user interfaces based on touch-sensitive sensing areas mistakes may be made in correctly determining which of the sensing areas is to be intended for selection (i.e. which areas are to be considered activated). Such mistakes may arise because the measurement signal values that are associated with the different sensing areas in a touch sensitive user interface (e.g. measurements of capacitance) are not generally binary indications, but are continuously variable. A controller is thus employed to analyze the measurement signal values for the various sensing areas and to determine which keys are to be considered as being currently activated from their associated measurement signals.
The general trend towards smaller interfaces with increased functionality increases the complexity of properly determining sensing areas intended to be selected. Smaller touch-sensitive user interfaces have more densely packed sensing areas such that a user's finger (or other pointing object) is more likely to overlap multiple keys at the same time or in too-quick succession. Furthermore, cover panels for touch-sensitive user interfaces are often flat such that there is no tactile feedback available to help a user to correctly position the pointing object over the desired region of the touch-sensitive user interface.
Basing key selection on a straightforward comparison of the magnitudes of the measured signal values, such as by selecting which key is currently associated with the greatest coupling signal above a selection threshold, does not always provide satisfactory performance. Even though some existing schemes may provide improved user-interface performance in many situations, there are still situations in which a user interfaces can be prone to error (e.g., by wrongly indicating that a sensing area (key) has been selected, when in fact a user did not intend to select this sensing area).